BGA or LGA IC sockets commonly have a large number of electrical contacts (hereinafter, simply referred to as “contacts”), arranged in a matrix along a bottom surface of an IC package receiving recess for electrically connecting with an IC package.
An example of such an IC socket is known a burn in socket. One such burn in socket is disclosed in Japanese Unexamined Utility Model Publication No. 5(1993)-90378 (FIG. 2). The burn in socket comprises a large number of contacts, which are located within an IC package receiving recess and arranged in a matrix. The contacts comprise transition sections that extend diagonally in a stepwise manner. Contact sections are formed at the free ends of the transition sections. The contact sections protrude into and are exposed within the IC package receiving recess of a housing.
Another conventional IC socket is disclosed in U.S. Pat. No. 4,761,140 (FIG. 2 and FIG. 3). This IC socket comprises rectangular contacts, which are provided along the four inner walls of an IC package receiving recess. The edges of free ends of the contacts are housed in the contact cavities, and do not protrude into the IC package receiving recess.
In the burn in socket disclosed in Japanese Unexamined Utility Model Publication No. 5(1993)-90378, the contact sections of the contacts protrude upwardly within the IC package receiving recess. Therefore, external objects, such as fingers and the like, may strike the exposed contact sections during mounting or dismounting of an IC package to or from the IC socket. This is particularly problematic in applications where the burn in socket is utilized to diagnose a CPU (central processing unit) of the IC package because the mounting and dismounting of the IC package is generally performed manually. When a finger strikes the contact sections of the contacts, there is a risk that the contact sections will plastically deform, thereby causing poor electrical contact between them and the IC package, when the IC package is mounted.
In the IC socket of U.S. Pat. No. 4,761,140, deformation of the contacts is prevented, because the edges of the free ends of the contacts are not engaged by a finger, even if a finger strikes the contacts. However, the size of the cavities, for housing the contacts, is relatively large, thereby causing a problem that the contacts cannot be arranged in a high density.